The invention relates to systems for filtering, i.e., separating, concentrating, and dewatering, relatively fine particles entrained in a fluid to thereby obtain a consolidated, semi-solid material or xe2x80x9csludge.xe2x80x9d
For example, a common technique for capturing paint overspray/airborne paint particulate produced when operating a paint spray booth is to capture such particulate in a waterfall backdrop within the spray booth. The resulting water-and-particulate fluid mixture is then channeled into a suitable filtration system in which the paint particulate is substantially removed from the water. The filtered water is thereafter advantageously recirculated back to the spray booth""s waterfall backdrop to capture more airborne paint particulate.
Such known filtration systems typically receive the water-and-particulate fluid mixture in a large collection tank or xe2x80x9cpit,xe2x80x9d for example, by gravity feed. The paint particulate is then separated, consolidated, and dewatered in a multistage process. By way of example, in a typical first separation stage, a supply of compressed air from an external source is directed through a diffusing nozzle assembly into the collection tank near the collection tank bottom. The supply of compressed air is provided, for example, at perhaps about 2 psig from a centrifugal blower, or at perhaps up to about 5 psig from a throttled plant compressed air supply, with the air delivery pressure generally being prescribed as a function of the depth at which the nozzle assembly is positioned below the surface of the fluid mixture collected in the collection tank.
The compressed air exits the nozzle assembly in the form of small bubbles which thereafter rise up to the surface of the collection tank. As the bubbles rise, the entrained particulate adheres to the bubbles through surface tension, and the particulate is gently carried by the bubbles up to the surface of the collection tank. A mechanical separator, such as a weir, positioned near the surface of the fluid collected in the collection tank, completes the first stage of the process by xe2x80x9cskimming offxe2x80x9d or separating the uppermost layers of water-laden particulate from the surface of the fluid. A pump thereafter transfers the separated water-laden particulate into a floatation consolidation tank, also known as a floatation consolidator or xe2x80x9cPalin,xe2x80x9d for a second stage of the filtration process.
Once in the consolidation tank, a typical second, consolidation stage begins, in which a further external supply of compressed air, similarly ranging up to about 5 psig and typically at or below ambient temperature, is directed through a diffusing nozzle positioned at a predetermined depth in the consolidation tank. Once again, the particulate is carried to the surface by the resulting air bubbles and, as more particulate rises, the raised particulate begins to build up above the nominal surface of the pool collected within the consolidation tank. As the rising bubbles percolate through the raised particulate layer, the rising bubbles further serve to aerate the raised particulate layer to release free water and thereby reduce the water content of the uppermost layers. A mechanical separator, such as a reciprocating surface scraper, periodically collects the uppermost layers that have xe2x80x9cconsolidatedxe2x80x9d proximate to the pool surface in preparation for the third and final stage of the filtration process.
The consolidated wet paint sludge is thereafter transferred, for example, via a chute onto a moving water-permeable filter medium of a vacuum filter assembly, whereupon the filter medium carries the consolidated wet paint sludge over one or more vacuum chambers. A vacuum producer, such as a centrifugal blower capable of generating a vacuum in the range of between 1 and 4 in.Hg, draws air from each vacuum chamber and, hence, operates to draw water from the wet paint sludge, resulting in the desired dewatered paint sludge. In a known variant, the blower""s discharge air is directed onto the wet paint sludge atop the filter medium as it traverses the ramp to further enhance the dewatering effect of the vacuum filter assembly.
It is an object of the invention to provide a system for filtering a fluid mixture including paint particulate and water that provides improved performance over such known filtration systems as described above while further eliminating the need for an external supply of compressed air with which to provide aeration of either the collection tank or the consolidation tank.
It is another object of the invention to provide a system for filtering a fluid mixture including paint particulate and water featuring an integrated vacuum producer capable of providing a supply of compressed air suitable for use in connection with collection and/or consolidation tank aeration at relatively greater depths than is typical of prior art filtration systems that employ an external supply of compressed air.
Under the invention, a system is provided for filtering a fluid mixture that includes paint spray particulate and water to obtain a consolidated and substantially dewatered paint sludge. The system includes a first, collection tank adapted to receive a supply of the fluid mixture, the collection tank having a skimmer that mechanically separates water-laden particles from a surface of the fluid mixture collected in the first tank.
The system also includes a second, floatation consolidation tank that receives the separated, water-laden particulate from the collection tank, the consolidation tank having a surface scraper for collecting particulate that consolidates proximate to a surface of a liquid pool formed in the bottom of the consolidation tank, whereby the collected-and-consolidated particulate forms a wet paint sludge.
The system further includes a dewatering vacuum filter assembly having a water-permeable filter medium that moves atop a ramp over at least one, and most preferably two, vacuum chambers. The wet paint sludge is received on the filter medium, whereupon the filter medium carries the wet paint sludge over each vacuum chamber while the chamber""s respective vacuum producer evacuates the vacuum chamber to thereby extract free water from the wet paint sludge.
In accordance with a feature of the invention, the first, xe2x80x9cwet rampxe2x80x9d vacuum producer is a rotary positive displacement blower discharging a first supply of pressurized air at a pressure greater than about 5 psig and a temperature of at least about 140xc2x0 F., and, most preferably, at a pressure greater than about 7 psig and a temperature greater than about 170xc2x0 F. Further, under the invention, at least one of the collection tank and the consolidation tank includes an aerating diffuser assembly receiving and discharging, into the collection tank or the consolidation tank at a predetermined depth beneath the surface of the fluid mixture or the surface of the pool, respectively, at least a portion of the first supply of pressurized air discharged from the positive displacement blower.
In accordance with another feature of the invention, in a preferred embodiment, a second, xe2x80x9cdry rampxe2x80x9d vacuum producer draws air from a second vacuum chamber disposed beneath the moving filter medium in series with the first vacuum chamber. The second vacuum producer which, in a constructed embodiment, is conveniently a centrifugal blower, generates a second supply of pressurized air at roughly ambient temperature and at a discharge pressure of up to about 4 psig. The second supply of pressurized air is directed onto the wet paint sludge atop the filter medium to thereby enhance dewatering.
Most preferably, the relatively-hotter first supply of pressurized air is heat exchanged with the relatively-cooler second supply of pressurized air, whereby the temperature of the second supply of pressurized air is elevated to enhance paint sludge dewatering. In a preferred embodiment, the system includes a cross-flow heat exchanger such that the exit temperature of the second supply of pressurized air, as routed through the heat exchanger, may be greater than the exit temperature of the first supply of pressurized air (before the latter is routed to the diffusing nozzle assembly of either the collection tank or the consolidation tank, or both of them).
Other features, benefits, and advantages of the invention will be apparent upon reviewing the following description of an exemplary system in accordance with the invention.
The Drawing is a diagrammatic view of an exemplary system for separating, consolidating, and dewatering a fluid mixture that includes paint spray particulate and water, in accordance with the invention.